Right click on a component instance to open the context menu.
Select SNMP and then click on supported MIBs.
When you assign a SNMP MIB file to a component definition, all future component instances of that definition will have the MIBs assigned to them.
You can view your selected component instance here (1).
You can view and manage the MIB files here (2).
For more information about managing MIB files, go to: Manage MIBs